Add background image support to header components

Updated header components to accept and render background images via a new `[background_image]` input property. Modified relevant templates to apply the background image dynamically and updated usage in `home` and `map` components.

frontend/src/app/header/header.component.html

@@ -1,5 +1,5 @@
 <ng-container>
-  <header id="top">
+  <header id="top" [ngStyle]="{ 'background-image': 'url(' + background_image + ')'}">
     <nav id="nav" [ngClass]="active">
       <div class="container">
         <div id="mobile_nav">

frontend/src/app/header/header.component.ts

@@ -11,6 +11,7 @@ export class HeaderComponent {
   @Input() title: string = '';
   @Input() sub_title: string = '';
   @Input() current_page: string = '';
+  @Input() background_image: string = '';
 
   public active: string = '';